The present invention relates generally to a method for removing halogenated organic compounds from organic fluids containing same and more particularly to a method for removing PCBs from functional fluids, such as transformer oil, contaminated therewith.
The potential hazard to health and the environment posed by synthetic halogen-containing organic chemicals is well known. Compounds such as polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), decachlorooctahydro-1,3,4-metheno-2H-cyclobuta-[c,d]-pentalen-2-one (Kepone.RTM.), and 2,4,5-trichlorophenoxyacetic acid, (2,4,5-T), although having demonstrated utility, have been found to be persistent environmental toxins which require safe and effective means of disposal.
Halogenated organic compounds present a difficult disposal problem because of the highly stable nature of the carbon-halogen bonds present therein. The bond energy of a carbon-chlorine bond, for example, is on the order of eighty-four kcal./mole. Thus, many halogenated organic compounds are not only resistant to biodegradation, they cannot be degraded in a practical and effective manner by way of the well known chemical decomposition methods. In most cases, known detoxifying methods such as chlorolysis, catalytic dehydrohalogenation, molten salt reactions, ozone reactions and alkali metal reduction achieve only partial dehalogenation. Moreover, these prior art methods typically involve one or more drawbacks, such as the use of expensive reagents, extensive temperature control, inert atmospheres, complex apparatus, substantial energy consumption and the like.
A particularly troublesome problem is presented when the halogenated organic compound is present as a contaminant in an otherwise useful functional fluid. For instance, PCBs were once widely used as a dielectric fluid in electrical equipment such as transformers and capacitors because of their excellent insulating properties. In 1977, however, all production of PCBs was stopped due to their cumulative storage in human fatty tissue and reports of extremely high toxicity. PCBs were replaced as a dielectric fluid with other less harmful substances. These latter substances have since been found to contain residual amounts of PCBs therein. Consequently, the maintenance, operation and disposal of PCB-contaminated transformers and transformer oil is now strictly regulated.
Since the production ban on PCBs, incineration has probably been the most widely used method for destroying PCBs and PCB--contaminated materials. Disposal by incineration is decidedly wasteful, however, since potentially recyclable materials, such as functional fluids, are destroyed in the process. To avoid such waste, methods have been proposed whereby PCB-contaminated materials in particular would be treated with an adsorbant, e.g., by passing the material through a bed of activated charcoal or resin to selectively remove the PCBs from said material. Although PCBs are physically removed from the recyclable material in this manner, the disposal of adsorbed PCBs still remains a problem.
During the past several years, there has been developed at the Franklin Research Center of the Franklin Institute, Philadelphia, Pennsylvania, a system for stripping the chlorine substituents from various halogenated organic compounds, including PCBs, thus rendering them non-toxic and readily disposable. More specifically, Pytlewski, Krevitz and Smith, in their U.S. patent application Ser. No. 158,359, filed June 11, 1980, now U.S. Pat. No. 4,337,368, disclose and claim a method for the decomposition of halogenated organic compounds, which represents a significant advance over the aforementioned decomposition methods of the prior art. The decomposition reagent used in practicing the method of Pytlewski et al. is formed from the reaction between an alkali metal, a liquid reactant, such as polyglycol or a polyglycol monoalkyl ether, and oxygen. This reagent produces virtually complete dehalogenation simply by mixing it with the halogenated compound in the presence of oxygen.
In U.S. patent application Ser. No. 240,622, filed Mar. 5, 1981, there is described and claimed another invention by Pytlewski et al. based on the discovery that decomposition of halogenated organic compounds may be carried out using a reagent produced by the reaction of an alkali metal hydroxide (rather than an alkali metal), a liquid reagent, such as a polyglycol or a polyglycol monalkyl ether, and oxygen. This decomposition reagent gives results which are comparable to those obtained with the method described in the earlier filed application of Pytlewski et al. referred to above.
The decomposition reagents of the aforesaid patent applications are collectively referred to hereinafter as NaPEG reagents, or simply NaPEG, and the expression "decomposition reagent", as used herein, refers to these NaPEG reagents.
The development of the NaPEG reagents has made it possible to remove various halogenated organic compounds, including PCBs, from fluids contaminated therewith, as well as to decompose such compounds in concentrated form in a safe, efficient and effective manner. However, as disclosed in our aforementioned patent applications, it was believed, prior to the present invention, that in order for decomposition to occur using NaPEG it was essential that the decomposition reaction be carried out in the presence of oxygen, since attempts at operating in an inert atmosphere were found to be unsuccessful.